CD4069UB

[sprog]

Will this work for an unbuffered CMOS inverter, like the CD4049? I'm trying to learn about clipping, and am interested in the Hot Harmonics clipping section because it seems gentle on the signal. I wanted to sample some CD4049UBE's, but TI did not offer them. I looked through TI's product tree & came up with this. Is it the same? I'm a newbie, can you please help me?

[SonicVI]

Yes, Yamaha had a pedal in the 80's called the COD-100 CMOS Overdrive that used the 4069.

[sprog]

So I could use it for the hot harmonics clipping section? Thanks....

[gez]

Is it the same?

The pinout is different (see data sheet), but the chip will give you soft clipping just like a 4049UB.

[sprog]

Excellent... thanks for the info. TI will sample those out. 

[Mark Hammer]

In fact a number of Laney amps use the 4069 for their preamp overdrive sections, so you're in good company.

[gez]

And those Laneys have a cracking* overdrive sound! (used to play through one on a regular basis).

* Just realised that this might be missinterpreted - UK expression for excellent.

[sprog]

Well, I went back to TI's website today & the samples section is totally different & my shopping cart was emptied. Now they do not have these 4069's any more. 

So, can I use any hex inverter for the soft clipping, as long as it is unbuffered (which makes no sense to me because it is a buffer... I've been reading a lot here lately)?

[R.G.]

The 4069 is not a buffer. It's an inverter.

The CD4049 is an inverting buffer. The CD4050 is a buffer. These are the overall designations.


In the CMOS logic chips, the original chips were just the logic function. They found out that this severely limited the speed when driving several other gates. So they put buffers on the outputs, big burly current drivers that also had lots of voltage gain. That ensured that even with limited inputs, the outputs would bang from ground to Vdd solidly, perfect for logic. This internal buffer in the logic chip made it better for logic, but worse for analog uses.

So we have to hunt down the unbuffered chips for analog.

You can also use the CD4049UB for distortion. The CD4049B will not work well.

[Mark Hammer]

Here is the overdrive section from the Laney HCM15R, a small TDA2030-powered amp.

There are different versions of the switching circuit (to go from overdrive to clean).  This one is manual, while others are FET-based. 

After the point on the right where one selects between clean and overdrive, there is an op-amp buffer followed by a fairly standard T/M/B tonestack.  While the op-amp is powered by +/-15v in the schematic, the 4069 is powered by +5v.  For adapting to pedal purposes, the TL072 could easily be powered by +9v with a floating ground (4.5 Vref).

A few key things about the overdrive section.  First off, where it looks like it says .1M (which you might think = 100k) in the first screenshot, it is actually 1M as you can see in the second one.  Secondly, the first schematic indicates use of a dual-ganged 100k drive pot that is log for one section and linear for the other.  Yeah, good luck snagging that one.   The lower schematic, which is the identical circuit, indicates that both section are log, a MUCH more common part.

Because the input op-amp buffer provides for a) minimal gain and no tone shaping, and b) a parallel clean output with level control (the 470pf compensating cap for the volume pot can be omitted if you want), you could easily adapt the circuit to be an "always buffered" overdrive where all you need the stompbox to do is select between the output of the clean volume pot and the output of the drive volume pot.  My sense is that the resistors after the wiper of each of those pots are simply for purposes of where they tie to the mixer stage.  If you are taking your output from each wiper, those extra resistors are unnecessary. 

On the other hand, since there are two signals that the schematic suggests can be blended, use a TL072 for the input buffer and a post-drive mixer stage and you can make your own 4069-based "Sparkle Drive"-type pedal, with blendable clean and dirty signals.  Naturally, in that case, you would need to bypass the entire circuit, rather than simply select between outputs coming from the overdrive and clean stages.

Now, I have absolutely no idea how this sounds in the amp, or how it would sound as a pedal, but Gez/Gerry has refined tastes and much knowledge, so if he gives thumbs up to the Laney overdrive (though how much is the 4069 and how much the speaker is another matter), then it is worth a try.

If anyone builds this and likes it enough to post a layout, I would make one simple request.  Name it after my sister, whom my children refer to as "Auntie Laney" (her name is Elaine).  Her neighbourhood is currently under water from spring run-off and she could use a smile.

[gez]

Refined, I like that...